Cooling water systems are found in many different commercial and industrial installations, including power generating stations, petroleum refineries, steel mills, chemical plants, textile plants, commercial refrigeration plants and central air-conditioning systems for office buildings and factories. At these installations three principal types of cooling systems are used.
Once-through systems are sometimes used in which water is taken from a primary source, is used for cooling, and is then discharged into waste or thereafter is used for other purposes.
The second type of cooling water system is a "closed recirculating system" in which all water is continually recycled and heat is removed by means of a heat exchanger that may be cooled by air, a refrigerant gas such as freon or by a separate open cooling system.
The third type of cooling water system is an "open recirculating system" in which a main portion of the water used for process cooling is continuously recycled to an evaporative cooling device such as a cooling tower whereby heat is removed from the processed water where it is returned for cooling purposes. The present invention concerns this type of open recirculating cooling water system.
Open recirculating water systems are frequently used because they not only provide economical heat removal but by recirculation of the water conservation is accomplished with substantial cost reductions. Additionally, less chemicals are used for treatment of the water which also provides for savings. The only water lost from such a system is lost by evaporation in the removal of excess heat, droplets of water captured by the moving air during cooling and the water removed by intentional or accidental purging of the system. Thus the amount of water required for makeup is reduced and money saved.
All water contains small amounts of dissolved solids that will deposit as scale on heat trasfer surfaces if allowed to concentrate in the circulating water of cooling water systems. As a result of the evaporation of circulating water in such systems as it passes through a cooling tower or the like the dissolved solids concentrate in the basin water. As these concentrates increase, additional amounts of chemicals are added to hold the dissolved solids in suspension. The cost of chemically treating the water can be prohibitive and a point is reached where the dissolved solids become so concentrated that chemical treatment is ineffective.
Fresh or makeup water is relatively low in dissolved solids and therefore can be used to dilute the highly concentrated basin water to thereby lower the dissolved solids content. Water can be drained off to waste in order to maintain an acceptable level of dissolved solids without chemical treatment. However, the cost of the water lost by using this procedure can become excessive and usually a limited controlled amount of water is "bled-off" while chemical treatment is being applied to the remaining water and this procedure has been found to be economically sound. The proper balance between the amount of bleed-off and the extent of chemical treatment occurs when the amount of dissolved solids in the circulating water is maintained at between three and five times the normal concentration of the fresh or makeup water. To maintain these concentration levels the bleed-off water should be approximately one-half to one gallon per hour per ton of refrigeration (or its equivalent) capacity. Thus, a ten ton capacity system would have to have five to ten gallons of basin water per hour "bled-off" to hold the solids concentration within the three to five multiple range.
Heat from any process such as a building is transferred to the circulating cooling water through a gas or liquid media and the heat is then transferred primarily by the water vapor in the air. Since the latent heat of vaporization of water is 1,000 BTU's per pound, each pound of water evaporated will absorb 1,000 BTU's from the heat transfer system. A total heat content of 15,000 BTU's per hour evaporated is one ton of refrigeration. To absorb 15,000 BTU's of heat per hour requires the vaporization of 15 pounds of water per hour, 15,000.div.1,000=15 lbs. and 15 lbs..div.8.35 lbs./gallons =1.8 gallons of refrigerating capacity. A ten ton cooling unit would therefore have an evaporation loss of 18 gallons, 150 pounds of water or 150,000 BTU's (18.times.8.35=150 lbs..times.1000).
Hence a ten ton cooling unit operating at full load capacity requires the evaporation of 18 gallons of water per hour with a bleed-off of 5-10 gallons of water per hour or 18.div.5 to 10=3.6 to 1.8. Thus, for each 1.8 to 3.6 gallons of water evaporated, one gallon must be bled-off to maintain the cycles of concentration desired for a ten ton unit.
Thus, in the United States, air conditioning and refrigerating systems are rated in "tons" and an evaporative cooling ton is equivalent to a heat load of 15,000 BTU's per hour. Since a BTU is a measurement of heat, the temperature measurements provides a convenient and accurate measurement of system tonnage and bleed-off.
In an effort to maintain the proper cycles of concentration of chemical balance in the recirculating water, prior devices and methods have employed conductivity or resistant measurement, pH probes, intermittantly activated water meters, timers and other devices. However, none of the methods or systems which have been in use in the past provide the desired results and they have not established the necessary mathematical relationship between evaporation in BTU's, heat load upon the system, bleed-off and/or modulating between no load and full load tonnage of the system, automatically.
Conductivity and resistance devices also measure or read the chemicals introduced to prevent corrosion, scale, and microbiological growths. Often the chemicals used exceed the natural total dissolved solids and can mask the readings of the circulating water taken thus causing excessive bleed-off. Chemically speaking there is no mathematical relationship between conductivity or resistance of basin circulating water and tons of refrigeration/bleed-off as measured in gallons or pounds or BTU's.
Timing devices cannot modulate between no load and full load tonnage capacity and such timers are only correct twice daily and are only effective under fixed prescribed conditions.
With this background in mind the present invention was conceived and one of its objectives is to provide an efficient and easily monitored system for maintaining the totally dissolved solids in the recirculating water at any desired level of concentration.
It is another objective of the present invention to conserve energy and to reduce the amount of treated water which is bled-off by improving the sensitivity and efficiency over known systems.
It is still another objective of the present invention to provide a method for automatic blowdown to prevent an excessive buildup of dissolved solids or undesired materials in the recirculating water by maintaining a desired mathematical ratio between the evaporated to bleed-off water.
Another objective of the present invention is to provide a method for blowdown which is easily adjusted to conform to 1.degree. F. for temperature changes of the circulating water temperature and to modulate between no load and full load tonnage of the system automatically.
It is still another objective of the present invention to provide a blowdown method which will add makeup water in direct proportion to the amount of blowdown, automatically.
Another objective of the present invention is to provide a fail-system to shut down during power failures.
Also an objective of the present invention is to provide a blowdown system of one convenient size which will fit practically all circulating water systems regardless of their size or capacity.
Various other objectives and advantages of the present invention will become apparent to those skilled in the art upon review of the detailed description of the invention as set forth below.